1. Field of the Invention
The present invention relates to a loaded weight measurement method and loaded weight measurement device for a dump truck.
2. Description of the Related Art
A method is known in the prior art (Japanese Patent Laid-open No. 61-34425) in which the weight of cargo is measured by detecting the load applied respectively to the front wheels and the rear wheels of a dump truck and correcting these detected loads on the basis of the angle of inclination of the vehicle and the center of gravity of the vehicle.
According to the prior art technology described in Japanese Patent Laid-open No. 61-34425, it is possible to determine the weight of a cargo simply by detecting the loads applied respectively to the front wheels and rear wheels. However, this conventional technology can only be applied to a dump truck having respective left and right-hand pairs of wheels in the front and rear portions of the vehicle body. Therefore, it is difficult to apply directly to a dump truck having two pairs of wheels in either the front section or rear section, as in the case of an articulated dump truck, for instance.
For example, in the case of an articulated dump truck, respective left and right-hand pairs of front wheels, central wheels and rear wheels are provided. The weight of an articulated dump truck is supported in a divided fashion by the front wheels, the central wheels and the rear wheels. Therefore, in order to measure the weight of cargo loaded into the vessel of the truck accurately, it is necessary to measure the respective loads applied to the front wheels, central wheels and rear wheels.
Here, for example, if the front wheels and the rear wheels are supported respectively by suspension cylinders, and the central wheels are supported by springs, then it is difficult to detect the load applied to the central wheels, accurately. A method can be conceived in which the amount of compression of the springs supporting the central wheels is measured and the load is determined on the basis of this amount of compression. However, this method produces significant error in the measurement of the loaded weight. The relationship between the compression of the springs and the load varies due to the effects friction in the springs, and other factors.
Therefore, a method may be conceived in which the central wheels are also supported by suspension cylinders, instead of springs, the load applied to the central wheels being measured by means of pressure sensors provided in these suspension cylinders. However, suspension cylinders are expensive compared to springs, and since pressure sensors must also be provided, the manufacturing costs of the dump truck increase.
The aforementioned problems are not limited to the case of articulated dump trucks, and are also common to dump trucks which have two pairs of wheels supported on rotatable equalizer bars, in at least the front or rear portion of the vehicle body.